Green algae is a large paraphyletic group of algae from which the higher plants (the embryophytes) developed. There are over 7,000 known species of green algae and green algae can be found in a wide range of different habitats all over the world. A majority of the species are unicellular or filamentous algae living in freshwater, but other forms of green algae exists as well and you can find green algae in both saltwater and brackish environments.
Almost all known forms of green algae are equipped with chloroplast filled with chlorophyll a and chlorophyll b, just like higher plants, and this is why they are green. Green algae also contain the secondary pigments in the form of carotenes, lutein and zeaxanthin, and sometimes even siphonoxanthin. Another similarity between higher plants and green algae is that they both store starch (amylose or amylopectin).
Green algae will typically have cellulose in their cell walls and all species have mitochondria with flat cristae. Quite a lot of the species are flagellates with two flagella for each cell, which makes it possible for them to propel themselves. The flagella are normally anchored by microtubules, but there are exceptions to this general rule.
As mentioned above, green algae can be unicellular or form colonies. In members of the order Charales, which are comparatively close relatives of the higher plants, full differentiation of tissues do occur.
Green algae in the aquarium
You might find green algae unsightly, but it is actually part of the natural ecosystem in the aquarium and your fish won’t mind sharing their home with some green algae. On the contrary, many fish species and other aquatic creatures enjoy grazing green algae and having natural algae growth in your aquarium makes it possible for them to carry out their natural behaviour in captivity.
Many other types of algae, e.g. hair algae, is a signal to the aquarist that something has gone wrong with the water quality, but green algae is known to occur even in aquariums with perfect water quality. If the green algae start growing much faster than before, there is however a few things you can do to keep the algae growth in check.
The green alga gets its energy from photosynthesis and will therefore depend on light for its survival. Reducing the amount of light that reaches the aquarium can hamper the growth of green algae.
Green algae use the same type of nutrient as higher plants and including a lot of live plants in the set up will therefore force the algae to compete for food. In addition to this, it is important to carry out regular water changes and avoid over-feeding. Do not let the levels of organic waste rise, because this can easily lead to excessive algae growth in the aquarium.
- Manual cleaning
You can manually clean away the green algae, but you have to be persistent because it will soon be back again. Manual cleaning should therefore ideally be combined with other types of algae prevention, e.g. keeping the levels of organic waste down.
- Algae eaters
There are many creatures that love to feast on green algae. Before you get algae eaters for your aquarium, make sure that they will appreciate the tank mates, water chemistry, temperature, and so on, of your particular aquarium. Different algae eaters are ideal for different aquariums. Don’t limit yourself to fish only; sometimes snails or other invertebrates are a much better choice.
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